1. Field of the Invention
The present invention generally relates to night vision devices, and more specifically, to individual crew served weapon sights with thermal imagers or image intensifiers.
2. Description of Prior Art
Night vision devices such as weapon sights, goggles, binoculars and observation telescopes use a variety of light enhancement schemes, which convert faint or invisible light images to electron images. The image intensifier type uses an electron multiplier tube to amplify the electron output of a photocathode. Uncooled thermal imagers utilize a light absorbing laminate including a layer of ferroelectric and/or pyroelectric material which stores static images. These become dynamic electronic images when scanned by electron beams or charge-coupled readout devices. Far-infrared devices normally utilize arrays of exotic cryogenic photodiodes, immersed in liquid nitrogen, over which the light image is scanned by vibrating mirrors or the like. A common denominator of all of the above schemes is a phosphor screen at the user end of the device where the electronic image is converted to a fairly intense visible light image.
This image is viewed through a hooded eyepiece, which prevents any stray light from striking the users face or nearby objects. Such illumination could easily be detected by enemy devices, particularly an image intensifier. This requires, however, that the user not turn on the device until his face is firmly against the eyepiece. Also, his face must not be removed until the device is turned off. To assure these requirements a special hooded device has been devised with a pressure sensitive switch to detect facial contact. An electrical interface between the eyepiece and the device must also be present to turn the latter on and off in accordance with the state of the pressure switch.
Unfortunately, all imagers do not have such an interface. On the other hand, some devices may have an interface, and may also require an adapter for the eyepiece that obviates the interface. A further problem with the above arrangement is that electronic failures can be related to unnecessary switching of image intensifiers and the like. Finally the provision of such an interface complicates structure of the device making it less reliable and more difficult to maintain.